Field of the Invention
The invention relates to an optical multichannel transmission and/or reception module, in particular for high-bitrate digital optical signals.
Description of Related Art
Multichannel optical transmission and/or reception modules generally have two interfaces: The electric signals to be sent come in, and if necessary additional control signals or management signals for the module come in and go out, through an electric interface. Obviously, the electric interface can also act as the power supply for the module. The module can process the electric signals coming into it in a predetermined way and can then feed the processed signals into a driver unit, which in turn feeds the respective electric channel signal to an assigned electro-optic transmission element, such as a semiconductor laser. The electro-optic transmission element converts the electric signal fed to it by the driver unit into a corresponding optical channel signal and then feeds that to an optical output port on the module, wherein the module's optical output ports form an optical interface. Similarly, the module's optical interface can have multiple optical input ports, and an optical signal fed to an optical input port is in turn fed to an assigned opto-electric reception element, which converts the optical signal into a corresponding electric signal. The received electric signal is fed to a booster unit that boosts the received electric signal and feeds it to one or more units downstream for further processing, such as clock-and-data recovery (CDR). The processed electric signals are then fed to the electric interface.
The electric interface can obviously also be configured to feed and receive control or management signals that are needed for the receiver path. The electric interface can also provide a separate power supply for the receiver path.
When developing a design for such a multichannel transmission and/or reception module, it is necessary to configure the optical paths between the output ports of the electro-optic transmission elements and the optical output ports of the module or between the optical input ports of the module and the optical input ports of the opto-electric receiving elements as simply as possible, to reduce signal loss and allow cost-effective manufacturing. It is already known how to generate optical paths through multiple optical waveguides, such as glass fibers, wherein the ends of the optical wave guides must be positioned precisely with respect to the positions of the respective ports on the transmission elements or reception elements. In addition, the waveguide ends are often connected to the respective ports on the transmission or reception elements using free optical path segments within which there is no channeling of the optical signals through a waveguide. This requires sealed housings for multichannel transmission and/or reception modules configured in that manner, which makes them more expensive to manufacture.
Optical paths created using optical waveguides are therefore generally designed to run as straight as possible, for the least possible dampening of the optical paths due to macrobending of the optical waveguides. Because optical multichannel transmission and/or reception modules are often configured so that they can be placed in respective insertion locations of superordinate communication devices as needed, most multichannel transmission and/or reception modules have a standardized housing, usually consisting of an oblong, essentially rectangular structure. The optic and electric interfaces are located on the shortest front sides. The electric interface is located on the front side that projects into the superordinate communication device. The respective external fiber-optic cables can then be connected to the optic interface on the opposite front side.
The housing of such an optical multichannel transmission and/or reception module can contain an assembly, such as a circuit board, on which all the components needed to transmit and receive the optical signals are located. In addition, this assembly can also include all other electric and/or electronic components needed to pre-process the (electric) signals to be transmitted and to control the electro-optic transmission elements that convert the pre-processed (electric) signals into the corresponding optical signals. The same also applies to the electric and/or electronic components needed for further processing of the electric signals received from the opto-electric reception elements (i.e., the optically/electrically converted optical reception signals).
This assembly or the related (usually printed) circuit board is generally placed lengthwise in the module housing. One end of the lengthwise-placed circuit board can therefore also serve as the location for connecting the electric interface.
In this arrangement, the electro-optic transmission elements or opto-electric reception elements are incorporated into the assembly in such a way that the optic waveguides run between the module's optic interface, which is generally an optical unit plugged into the appropriate module end, and the transmission or reception elements, generally in a straight line along the longitudinal axis of the housing or parallel to the plane of the assembly's printed circuit board.
It is also possible to incorporate this assembly into an opto-electric assembly (hereinafter called an opto-electric module) and a purely electric assembly. The opto-electric assembly includes the electro-optic transmission elements or opto-electric reception elements and, if necessary, other electric or electronic components such as driver units for the electro-optic transmission elements and electric booster units for the opto-electric reception elements, which should be positioned as close as possible to the transmission or reception elements. This opto-electric module is connected through an internal electric interface to the purely electric assembly that includes the additional components needed to pre-process or further process the respective electric signals.
US 2011/0216998 A1 describes an opto-electric sub-assembly in the form of an optic wafer, on which there are multiple optical paths in a transparent flat (even) substrate between the outer surfaces that lie opposite each other, wherein each optical path has surfaces that interface with the substrate's outer surfaces, which are positioned precisely with respect to corresponding reference markers. For positioning electro-optic transmission elements or opto-electric reception elements with respect to the interface surfaces of the optical paths, mechanical positioning means are provided that allow these elements to be positioned relative to the reference markers located on the related wafer surfaces. This makes it possible to position the optical output ports of the transmission element or the optical input ports of the receiving element precisely with respect to the interface surfaces of the respective associated optical paths. Similarly, mechanical positioning means are provided on the opposing wafer surfaces, allowing an optical multi-connector to be positioned with respect to the interface surfaces of the optical paths. These wafer surfaces also have reference markers, relative to which the interface surfaces of the optical paths are positioned. Aligning the mechanical positioning means, such as a matching ferrule in a multi-connector, relative to the reference markers also permits easy positioning of all waveguide ends relative to the interface surfaces of the optical paths.
This opto-electric subassembly therefore allows for easy coupling of multiple optical waveguide ends to electro-optic transmission elements or opto-electric reception elements, and in particular of multiple transmission elements or reception elements that can be configured as arrays. This prevents free optical path segments.
If such an opto-electric subassembly is used in making an opto-electric module for an optic multichannel transmission and/or reception module, that module could be connected to the purely electric assembly in the usual way, using a slot provided in the purely electric assembly. The flat opto-electric module would then be essentially perpendicular to the lengthwise plane of the purely electric assembly, which runs parallel to the longitudinal axis of the housing.
At the same time, this would make it possible for the optical waveguides to run essentially straight or with only slight bends between the respective input and output ports (i.e., the axes of the optical waveguides must bend only with relatively large bending radii and small wrap angles) when connecting the opto-electric module and the input or output port of the transmission and/or reception module. This results in a minimal optic waveguide length. In addition, the essentially straight path results in little or no additional damping due to macro-bends.
Because the dimensions of such an opto-electric module cannot be arbitrarily small, due to the dimensions of the required electro-optic transmission elements or opto-electric reception elements, the housing of such a multichannel optical transmission and/or reception module must have a height or clearance that is greater than the measurements of the flat opto-electronic module in the “flat” plane, if it is placed in that cross-section of the housing.
However, newer standards for optical multichannel transmission and/or reception modules, in particular modules for generating or receiving high-bitrate optical signals, provide for housings with ever smaller dimensions. Nonetheless, the integration of electric and opto-electric assemblies or modules in such small housings represents an ever more demanding task.